This invention relates to feedforward amplifiers such as may be used in coaxial line transmission systems.
Feedforward amplifiers may be generally defined as having main and auxiliary amplifier stages in separate amplifying channels connected in parallel between common input and output terminals, each amplifier stage having its own negative feedback path, with a cross connection between the output of the main amplifier stage and the input of the auxiliary amplifier stage. The various connection between the two channels and the terminals are conveniently made by way of directional couplers which provide isolation between the different parts of the circuits where required.
In long distance coaxial line transmission systems, e.g. in submarine systems, it is necessary to reduce the effects of 3rd order intermodulation vectors. One convenient method of doing this is to introduce phase scattering of the vectors along the system. Alternatively intermodulation products could be cancelled at the end of the system.